There is a continuous demand for smaller and yet efficient internal mobile terminal antennas. The Planar Inverted F-Antenna (PIFA) has become a widely used antenna type by several mobile terminal manufacturers. Reasons for such widespread use include design, cost, and mechanical robustness. However, antenna efficiency may be reduced due to radiation levels emitted from the back of the mobile terminal (toward a user holding the mobile terminal to the ear) as compared with the front of the mobile terminal (away from a user holding the mobile terminal to the ear). In the low cellular bands, a major part of this radiation may originate from the ground plane, on a printed circuit board within a housing of a mobile terminal. It has been shown that at 900 MHz, around 90% of the radiation may come from the ground plane.
Certain antenna configurations may be used to increase operating efficiency. One such configuration, for example, is discussed by Mads Sager et al. in “A Novel Technique To Increase The Realized Efficiency Of A Mobile Phone Antenna Placed Beside A Head-Phantom” (IEEE 2003), the disclosure of which is hereby incorporated herein by reference in its entirety. Sager et al. discloses a dual-band PIFA mounted on the backside of a printed circuit board, and a parasitic radiator mounted on the front side of the printed circuit board. The length of the parasitic radiator can be adjusted for reduction of radiation toward the head of the user. However, the length of the parasitic radiator, and thus its maximum effectiveness, may be limited by the physical dimensions of the mobile terminal.